Transcriptional and biochemical analyses of gibberellin expression and content in germinated barley grain.

Vincent Bulone,Helen M Collins,Oliver Berkowitz,Qiongxian Lu,Natalie S Betts,Christoph Dockter,Michelle Hooi,James Whelan,Rachel A Burton,Geoffrey B Fincher,Birgitte Skadhauge,Gerhard Leubner

doi:10.1093/jxb/erz546

Abstract

Mobilization of reserves in germinated cereal grains is critical for early seedling vigour, global crop productivity, and hence food security. Gibberellins (GAs) are central to this process. We have developed a spatio-temporal model that describes the multifaceted mechanisms of GA regulation in germinated barley grain. The model was generated using RNA sequencing transcript data from tissues dissected from intact, germinated grain, which closely match measurements of GA hormones and their metabolites in those tissues. The data show that successful grain germination is underpinned by high concentrations of GA precursors in ungerminated grain, the use of independent metabolic pathways for the synthesis of several bioactive GAs during germination, and a capacity to abort bioactive GA biosynthesis. The most abundant bioactive form is GA1, which is synthesized in the scutellum as a glycosyl conjugate that diffuses to the aleurone, where it stimulates de novo synthesis of a GA3 conjugate and GA4. Synthesis of bioactive GAs in the aleurone provides a mechanism that ensures the hormonal signal is relayed from the scutellum to the distal tip of the grain. The transcript data set of 33 421 genes used to define GA metabolism is available as a resource to analyse other physiological processes in germinated grain.

Highlights

The most abundant bioactive form is GA1, which is synthesized in the scutellum as a glycosyl conjugate that diffuses to the aleurone, where it stimulates de novo synthesis of a GA3 conjugate and GA4
The germination of barley (Hordeum vulgare) and other commercially important cereal and grass grains involves a complex set of interactions between the living aleurone and embryo tissues.The latter includes the scutellum and its associated scutellar epithelium layer, which lies at the interface of the embryo and the non-living starchy endosperm
Morphological changes show the different fates of the aleurone and scutellum epithelium Germination has been defined as the period between initiation of the process, achieved through wetting the grain, to the point of coleorhiza emergence (Bewley and Black, 1994)

Summary

Introduction

The germination of barley (Hordeum vulgare) and other commercially important cereal and grass grains involves a complex set of interactions between the living aleurone and embryo tissues.The latter includes the scutellum and its associated scutellar epithelium layer, which lies at the interface of the embryo and the non-living starchy endosperm. Following the release of dormancy, germination of the grain is initiated by the uptake of water, mostly through the micropylar region of the embryo (Bewley and Black, 1994). Gibberellin expression in germinated barley grain | 1871. Α-amylase enzyme activity (Gibbons, 1981; McFadden et al, 1988).As the GA diffuses along the grain, it induces gene expression in the living aleurone cells of the endosperm, which form a thin layer around the non-living starchy endosperm (Duffus and Cochrane, 1993; Aubert et al, 2018). Germinated cereal grains, in particular barley, have been used as the primary raw material for brewing beer and other alcoholic beverages for thousands of years

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